1. Field
Aspects of the invention relate to a method of forming a weakening into a component, and in particular to a laser formed weakening in a trim piece for an automotive vehicle.
2. Discussion of Related Art
The introduction of weakenings or weakening lines in a decorative composite is widely used in particular in automotive vehicle construction. Weakenings or weakening lines of this kind form regions in the decorative composite at which the decorative composite tears, for example, upon airbag deployment or in the event of a crash. In this regard, parts of the decorative composite fold away or move toward each other in a defined manner.
Weakenings of this kind were typically formed either by seams having a defined tearing resistance or by means of mechanical tools, for example knives, milling tools, drills or the like. However, one drawback with such processes is the lack of precision for producing high-quality decorative components. In addition, such mechanical tools wear out and must be replaced to ensure a uniform cutting pattern.
Therefore, other approaches have also been disclosed for the introduction of weakenings. For example, laser beams have been employed to produce weakenings into decorative components. However the energy that is input into the decorative component by the laser beams needs to be removed from the weakened point without further damage to the decorative component or its appearance. The same applies to the waste gases formed during the combustion of materials as a result of the energy input from the laser.
In any case, a weakening in the decorative component should have a defined tearing resistance and preferably be invisible from the outside throughout the lifetime of the decorative component or at least not significantly change its appearance after production.
Methods for the introduction of a weakening in a decorative component employing a plurality of laser beams can be divided into two groups. In the first group, a composite layer structure of the decorative component is produced and then a predetermined breaking line is introduced into the component. In the second group, individual layers of the decorative composite are provided with weakenings and these pre-weakened layers are then joined together in a final step to form a weakened decorative composite.
One drawback of the second group is that multiple processing stages result in additional costs. In addition, unavoidable joining tolerances or the displacement of material during the joining and before the curing of adhesive and/or primer coats result in greater visibility of the weakened regions on the visible side of the component.
The drawback of the first group is that the high energy input required when weakening a multilayer decorative composite by employing lasers results in unavoidable material burnup at least in partial layers of the decorative composite. In particular, in the region of the upholstered layer, waste gases from laser-treated foamed materials with closed pores are only able to escape through the hole created by the laser itself. In the case of upholstered layers made of textile nonwovens or spacer fabrics, once again, both the volume expansion due to the generation of waste gases and uncontrolled material burnup in the regions adjacent to the weakening cause a bulging of the weakenings beyond the extent desired. For example, adjacent weakenings may combine in an undesirable manner at least in the upholstered layer and excessively weaken the decorative composite. Further, bulging of the weakening can occur in the upholstered layer, and possibly the layers surrounding the upholstered layer, so that the weakening becomes visible on the decorative side.
In the light of these problems, DE 102 27 118 A1 describes a method for introducing weakenings into a decorative composite comprising a carrier layer, a foam layer and a decorative layer in which a weakening is produced by a sequence of grouped blind holes of different lengths and breadths in the decorative composite. In this method, the decorative composite is weakened by the periodic arrangement of groups of blind holes of different depths and lengths. The first group of blind holes extend through virtually the entire decorative composite and are followed along the weakening by the second group of blind holes which extend only partially through the decorative composite. This second group of blind holes is then again followed by a group of blind holes of the first group.
However, this method does not solve the problem of the bulging of the blind holes in the region of the upholstered layer.